“His stuff will play in the major leagues,” the Padres manager said recently of the 23-year-old right-handed starter.

But not now.

Smith on Wednesday night suffered his third bad start in as many major league appearances — a night after left-handed starter Clayton Richard impressed Padres staffers in his second rehab outing with Triple-A Tucson.

For the second time in his three outings, Smith failed to retire a hitter in the second inning as he gave up four runs on five hits and three walks (one intentional) in a span of 11 St. Louis hitters.

Immediately after the game, Smith was optioned to Triple-A Tucson.

“Right now, it’s time for Burch to go back and continue to grow as a pitcher,” said Black. “He’s going to be fine. He’s a major league talent.”

Meanwhile, Cardinals left-hander Tyler Lyons held the Padres to one run on four hits over seven innings in his major league debut as St. Louis scored a 5-3 victory in the rubber-match of a three-game series before 18,683 at Petco Park.

The only run charged against Lyons, who threw only 81 pitches, was a 438-foot, seventh-inning homer to center by Jedd Gyorko — the rookie second baseman’s fifth homer of May and the season.

The Padres scored twice in the ninth on Alexi Amarista’s two-run single off former Padres reliever Edward Mujica.

Smith, who was promoted from Double-A San Antonio on May 11 a week after the struggling Richard had gone on the disabled list with “intestinal issues,” has allowed 15 runs on 16 hits and six walks over a span of 7 1/3 innings in his three starts with the Padres.

That’s an earned-run average of 18.41. Opposing hitters are batting .432 against Smith with an .865 slugging percentage (four homers, a triple and two doubles) and a .512 on-base percentage. Plus, his fastball dropped several notches in velocity Wednesday night.

Smith retired Lyons on a line drive to left (in his first major league at-bat) to get out of the first with three runs in and the bases loaded. But he was pulled after Matt Carpenter and Carlos Beltran opened the second with singles.

When Black went to the mound to relieve Smith, he spent some time talking to the pitcher before summoning Tim Stauffer from the bullpen.

“We talked a little about the present, a little about the future,” Black said of his mid-game discussion with Smith on the mound.

“It was a learning experience,” said Smith. “I’m going take what I learned, the good and the bad and try to improve. I learned there’s a difference between a strike and a quality strike”

Stauffer followed Smith and allowed one run on eight hits over 5 2/3 innings — the longest outing by a National League relief pitcher this season. Stauffer struck out seven without walking a batter in the longest outing by a Padres reliever since 2008.

The question now becomes who starts Tuesday when the spot comes up in the rotation in Seattle. Richard was back in the Padres’ clubhouse Wednesday night, although Black earlier stopped short of saying Richard is ready to come off the DL.

Richard allowed two runs on six hits and no walks with four strikeouts Tuesday.

Padres Assistant General Manager A.J. Hinch was with Richard in Omaha.

“A.J. told me Clayton’s arm slot looked higher and he had better sink and velocity on his fastball than we saw in April,” said Black. “And Clayton feels good today.”